Back to EveryPatent.com
| United States Patent |
5,539,720
|
|
Aoi
|
July 23, 1996
|
Method and apparatus for driving light source by stored current value
and for processing information
Abstract
An optical information processing method according to the present invention
includes a first step of supplying a driving current to a light source so
as to emit a light beam, a second step of converging the light beam
emitted from the light source and irradiating the converged light beam
onto an optical recording medium, a third step of adjusting a focal point
of the light beam on the medium, a fourth step of adjusting the driving
current so that the power of the light beam is set to a predetermined
value in a state in which the focal point was adjusted a fifth step of
storing the value of the driving current which was adjusted in the fourth
step, and a sixth step of supplying the current of the value stored in the
fifth step to the light source so as to emit the light beam and scanning
the medium by the light beam, and thereby recording, reproducing, or
erasing information. An apparatus to embody the above method is also
disclosed.
| Inventors:
|
Aoi; Shigeru (Kawasaki, JP)
|
| Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
109112 |
| Filed:
|
August 17, 1993 |
Foreign Application Priority Data
| Oct 11, 1988[JP] | 63-256318 |
| Current U.S. Class: |
369/116; 369/100 |
| Intern'l Class: |
G11B 007/00 |
| Field of Search: |
369/54,58,59,100,106,110,116,124,111,121,122
346/762
235/454,438
|
References Cited
U.S. Patent Documents
| 4375067 | Feb., 1983 | Kitamura | 346/160.
|
| 4509156 | Apr., 1985 | Oharu et al. | 369/54.
|
| 4747091 | May., 1988 | Doi | 369/116.
|
| 4894817 | Jan., 1990 | Tanaka et al. | 235/454.
|
| 4907212 | Mar., 1990 | Pharris et al. | 369/54.
|
| 4989198 | Jan., 1991 | Kojima et al. | 369/116.
|
| 4998234 | Mar., 1991 | Rees et al. | 369/124.
|
| 5005164 | Apr., 1991 | Sakamoto et al. | 369/59.
|
| 5070495 | Dec., 1991 | Bletscher et al. | 369/116.
|
| 5113384 | May., 1992 | McDonald et al. | 369/54.
|
Other References
Patent Abstracts of Japan, Nov. 18, 1986, vol. 10, No. 341, Kokai No.
61-142,538, Jun. 1986.
Patent Abstracts of Japan, Mar. 28, 1987, vol. 11, No. 100, Kokai No.
61-250,849, Nov. 1986.
|
Primary Examiner: Hindi; Nabil Z.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
Parent Case Text
This application is a continuation of prior application Ser. No. 07/418,557
filed Oct. 10, 1989, now abandoned.
Claims
What is claimed is:
1. An optical information recording/reproducing method comprising:
a first step of supplying a driving current to a semiconductor laser to
emit a light beam;
a second step of converging the light beam emitted from the semiconductor
laser and irradiating the converged light beam onto a predetermined area
on an optical recording medium where no information is recorded;
a third step of performing focusing control to adjust focal points of the
light beam on the predetermined area of the recording medium;
a fourth step of adjusting the driving current in states in which the
focusing control is being performed, while monitoring power of the light
beam, to set the power of the light beam to a predetermined value required
for recording or reproducing information;
a fifth step of storing a value of the driving current supplied to the
semiconductor laser when the power of the light beam is set to the
predetermined value in said fourth step; and
a sixth step of supplying the driving current having the value stored in
said fifth step to the semiconductor laser to emit the light beam, and
scanning the recording medium with the light beam to thereby effect one of
recording of information on and reproducing of information from the
recording medium.
2. A method according to claim 1, wherein further comprising storing, in
said fourth and fifth steps, a plurality of driving current values
corresponding to a plurality of different values of the power of the light
beam, and selecting, in said sixth step, a driving current value
corresponding to a required power of the light beam among the plurality of
driving current values in accordance with current conditions, to supply
the selected driving current value to the semiconductor laser.
3. A method according to claim 1, further comprising executing said fourth
and fifth steps when the medium and the light beam are relatively moving.
4. A method according to claim 3, further comprising executing said fourth
and fifth steps during execution of tracking control of the light beam to
tracks formed on the medium.
5. A method according to claim 1, further comprising irradiating, in said
second step, the light beam onto a predetermined area on the medium where
no information is recorded.
6. A method according to claim 1, wherein the lit semiconductor laser is
pulse light up.
7. A method according to claim 1, further comprising executing said first
through fifth steps when a power source of the apparatus is turned on.
8. A method according to claim 1, further comprising executing said first
through fifth steps when the medium is being exchanged.
9. A method according to claim 1, further comprising a step of measuring
temperature of the semiconductor laser, and wherein said first through
fifth steps are executed when the temperature of the light source changes
by at least a predetermined value.
10. A method according to claim 1, further comprising a step of comparing
the value of the driving current which was adjusted in said fourth step
with a predetermined limit value and generating a warning when the current
value has reached the limit value.
11. An optical information recording/reproducing apparatus for irradiating
a converged light beam onto an optical recording medium and for effecting
one of recording of information on and reproducing of information from the
recording medium, said apparatus comprising:
a semiconductor laser for emitting the light beam to irradiate a
predetermined area on the recording medium where no information is
recorded;
a current source for supplying a driving current to said semiconductor
laser;
a servo circuit for performing focusing control to adjust focal points of
the light beam on the predetermined area of the recording medium;
a detector for detecting power of the light beam emitted from said
semiconductor laser in a state in which the focusing control is being
performed, and for producing detection outputs;
an automatic power control circuit for controlling driving current supplied
to said semiconductor laser in accordance with the outputs of said
detector to set the power of the light beam to a predetermined value
required for recording or reproducing information;
a memory for storing a value of the driving current supplied to said
semiconductor laser when said automatic power control circuit sets the
power of the light beam to the predetermined value in the state in which
the focal points have been adjusted, wherein said memory stores the value
of driving current prior to the recording or reproducing of information;
and
a controller for supplying the driving current having the value stored in
said memory to said semiconductor laser to emit the light beam, to thereby
effect one of recording of information on and reproducing of information
from the recording medium.
12. An apparatus according to claim 11, wherein said memory stores a
plurality of driving current values corresponding to a plurality of
different values of the power of the light beam, and selects one of the
plurality of driving current values, corresponding to a required power of
the light beam in accordance with current conditions, to supply the
selected driving current value to said semiconductor laser.
13. An apparatus according to claim 11, further comprising means for
executing tracking control of the light beam to tracks formed on the
medium.
14. An apparatus according to claim 11, further comprising means for
comparing the current value which is input to the memory with a
predetermined limit value and for generating a warning when the current
value has reached the limit value.
15. An apparatus according to claim 11, further comprising:
means for measuring temperature of said semiconductor laser; and
means for updating the current value stored in said memory when the
measured temperature has changed by at least a predetermined value.
16. An optical information erasing method comprising:
a first step of supplying a driving current to a semiconductor laser to
emit a light beam;
a second step of converging the light beam emitted from the semiconductor
laser and irradiating the converged light beam onto a predetermined area
on an optical recording medium where no information is recorded;
a third step of performing focusing control to adjust focal points of the
light beam on the predetermined area of the recording medium;
a fourth step of adjusting the driving current in states in which the
focusing control is being performed, while monitoring power of the light
beam, to set the power of the light beam to a predetermined value required
for erasing information;
a fifth step of storing the value of the driving current supplied to the
semiconductor laser when the power of the light beam is set to the
predetermined value in said fourth step; and
a sixth step of supplying the driving current having the value stored in
said fifth step to the semiconductor laser to emit the light beam, and
scanning the recording medium with the light beam to thereby effect
erasing of information on the recording medium.
17. An optical information erasing apparatus for irradiating a converged
light beam onto an optical recording medium and for erasing information
recorded on the recording medium, said apparatus comprising:
a semiconductor laser for emitting the light beam to irradiate a
predetermined area on the recording medium where no information is
recorded;
a current source for supplying a driving current to said semiconductor
laser;
a servo circuit for performing focusing control to adjust focal points of
the light beam on the predetermined area of the recording medium;
a detector for detecting power of the light beam emitted from said
semiconductor laser in a state in which the focusing control is being
performed, and for producing detection outputs;
an automatic power control circuit for controlling the driving current
supplied to said semiconductor laser in accordance with the outputs of
said detector, to set the power of the light beam to a predetermined value
required for erasing information;
a memory for storing a value of the driving current supplied to said
semiconductor laser when said automatic power control circuit sets the
power of the light beam to the predetermined value in the state in which
the focal points have been adjusted, wherein said memory stores the value
of the driving current prior to the erasing of information; and
a controller for supplying the driving current having the value stored in
said memory to said semiconductor laser to emit the light beam, and to
thereby effect erasing of information recorded on the recording medium.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical information processing method
and apparatus in which a light beam emitted from a light source is
converged and irradiated onto an optical recording medium, thereby
executing at least one of recording, reproducing, and erasing operations
of information.
2. Related Background Art
Hitherto, as large capacity memories which are used in computers or the
like, an optical card apparatus which can record and reproduce
information, an optical disk apparatus, a magneto optical disk apparatus
which can record, reproduce, and erase information, and the like have been
known. In the above apparatuses, recording and the like are also executed
by irradiating the light beam emitted from the light source onto an
optical recording medium. At this time, an output power of a semiconductor
laser or the like which is used as a light source fluctuates in
association with environmental changes in temperature and the like even
when a predetermined current is input. Therefore, in an apparatus
disclosed in, for instance, U.S. Pat. No. 4,509,156, what is called an
automatic power control (APC) in which an output power of a light source
is detected upon reproduction and the result of the detection is fed back
to the light source to thereby keep the output power constant is executed.
On the other hand, in such an apparatus, upon recording, an input current
value by the APC in the reproducing mode is held, the current of an amount
corresponding to an increase in power which is necessary to record is
added to the current held, and the resultant added current is supplied to
the light source.
However, in the above APC, a certain extent of time period is necessary
until the output power of the light source becomes stable. Therefore, in a
case when the output power of the light source must be switched at a high
speed, for instance, the powers of the light beam which are necessary to
record or the like on an inner track portion and an outer track portion
of, for instance, an optical disk differ and, further, in a case when
random access of the light beam is executed in the region between those
portions, the APC cannot sufficiently cope with such a case.
On the other hand, to solve the above inconvenience of the APC, there has
been proposed an apparatus in U.S. Pat. No. 4,747,091 in which a light
source is experimentally driven to emit the light prior to executing the
recording operation or the like, the relation between a driving current of
the light source and an output power is previously measured, and the
result of the measurement is stored. According to such an apparatus, upon
operation, the APC is not initially executed but a current of the stored
value is supplied to the light source, thereby realizing a prompt
switching of the light power.
However, in the measurement by the apparatus disclosed in U.S. Pat. No.
4,747,091, an accurate result is not always obtained. This is because
different from the measuring mode, in the recording operation or the like,
the light beam has been converged onto a medium and its reflected light is
returned to the light source and an output of the light source is changed
by the returned reflected light. That is, in the apparatus of U.S. Pat.
No. 4,747,091, there is a concern of on occurrence of a difference of the
relations between the driving current and the light power upon measurement
before the operation and upon actual measurement.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the problems of the
conventional techniques and to provide an optical information processing
method and apparatus in which an output power of a light source can be
accurately adjusted at a high speed.
The above object of the invention is accomplished by an optical information
processing method comprising:
a first step of supplying a driving current to a light source so as to emit
a light beam;
a second step of converging the light beam emitted from the light source
and irradiating the converged light beam onto an optical recording medium;
a third step of adjusting a focal point of the light beam on the medium;
a fourth step of adjusting the driving current so that the power of the
light beam is set to a predetermined value in a state in which the focal
point was adjusted;
a fifth step of storing the value of the driving current which was adjusted
in the fourth step; and
a sixth step of supplying the current of the value stored in the fifth step
to the light source so as to emit the light beam and scanning the medium
by the light beam, and thereby recording, reproducing, or erasing
information.
On the other hand, an apparatus to embody the above method comprises:
a light source to emit a light beam;
a current source to supply a driving current to the light source;
a servo circuit to adjust a focal point of the light beam on a medium;
a detector to detect a power of the light beam which is emitted from the
light source;
an automatic power control circuit to control the driving current which is
supplied to the light source in accordance with an output from the
detector so that the power of the light beam is set to a predetermined
value;
a memory to store a value of the driving current supplied to the light
source in a state in which the light beam of the predetermined power was
irradiated onto the medium and the focal point was adjusted; and
a controller for supplying the current of the value stored in the memory to
the light source so as to emit the light beam, and for recording,
reproducing, or erasing information.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a construction of an embodiment of an
optical information processing apparatus of the invention;
FIG. 2 is a diagram for explaining a state of adjustment of a laser light
quantity in the apparatus shown in FIG. 1; and
FIGS. 3 and 4 are flowcharts showing the operating steps of the apparatus
shown in FIG. 1, respectively.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a block diagram showing a construction of an embodiment of an
optical information processing apparatus of the invention. FIG. 2 is a
diagram showing a state of measurement of a laser light quantity in the
apparatus shown in FIG. 1. FIGS. 3 and 4 are flowcharts showing the
measuring steps.
In FIG. 1, reference numeral 1 denotes a disk of an optical information
recording medium. The disk 1 is rotated by a motor 2. The light emitted
from a semiconductor laser 4 is focused onto the disk 1 by an objective
lens 5. The light reflected by the disk 1 again passes through the
objective lens 5 and is photoelectrically converted by a sensor 6 and
amplified by a preamplifier 7. The signal is then separated into a
focusing error signal, a tracking error signal, and a reproduction
information signal by the preamplifier 7. The reproduction information
signal is digitized by a binarizing circuit 8 and demodulated to the data
signal by a demodulation circuit 9 and is transmitted to a host apparatus.
The recording data signal from the host apparatus is input to a modulation
circuit 13 and transferred to a laser driving circuit 14 and drives the
laser 4. The tracking error signal and the focusing error signal which
were output from the preamplifier 7 are input to a servo circuit 12. A
focusing error and a tracking error of an optical head 3 are controlled on
the basis of the tracking error signal and focusing error signal.
Reference numeral 11 denotes a control circuit of the information
recording and reproducing apparatus. The control circuit 11 controls the
apparatus on the basis of commands from the host apparatus. An address
detecting circuit 10 detects an address of the beam position on the disk
from an output of the demodulation cirucit 9.
The laser driving circuit 14 supplies a driving current to the
semiconductor laser 4. As disclosed in JP-A-54-10481 and U.S. Pat. No.
4,375,067, the laser driving circuit 14 has a photodetector for receiving
the light which is emitted from the back side of the semiconductor laser 4
and for detecting an output power of the laser 4. An output of the
photodetector is used to control the power of the laser beam which is
emitted from the semiconductor laser to a constant value. That is, the
laser driving circuit 14 includes an APC circuit.
The operation of the apparatus shown in FIG. 1 will be described with
reference to the flowchart of FIG. 3. When a power source of the apparatus
is turned on, although not shown, a check is made to see if a disk has
been set in the apparatus or not (step 102). If no disk is set,
discrimination to see if the disk has been inserted or not is continuously
executed (step 110). After the insertion condition of the disk was
detected, the disk is loaded (step 111). If the disk has been set (step
102), the control circuit 11 rotates the disk by the motor 2. If a
rotational speed of the disk has reached a stationary value, the control
circuit 11 generates a command to the laser driving circuit 14, thereby
driving the laser with a reproduction light quantity and executing the
focusing control and tracking control by the servo circuit 12 (step 103).
Thereafter, the laser performance which will be explained later in FIG. 4
is measured. A temperature of the laser at this time is measured by a
thermometer (not shown) and the measured value is set to T.sub.0 (step
104). After completion of the measurement of the laser performance, a
check is made to see if the reproducing, recording, or erasing operation
has been instructed or not (step 105). Each operation is executed on the
basis of its command (step 106). The laser temperature is again measured
and a check is made by the control circuit 11 to see if the laser
temperature at this time has changed or not by the predetermined
temperature T.sub.D (in this case, 5.degree. C.) from the temperature when
the preceding laser performance was measured or more (step 107). If the
temperature has changed by T.sub.D or more, the laser performance is again
measured. If the temperature does not change, the control circuit 11
discriminates whether discharge of the disk has been instructed or not
(step 108). If NO, a check is again made to see if the reproducing,
recording, or erasing operation has been instructed or not. If the disk
discharge has been instructed, the control circuit 11 stops the tracking
and focusing controls by the servo circuit 12 and outputs a command to the
laser driving circuit 14 so as to stop the driving of the laser. The
rotation of the disk is stopped and the disk is discharged (step 109).
Thereafter, a check is again made to see if a disk has been loaded or not
(step 110).
The laser performance is measured in a state in which the focusing and
tracking controls are being executed in a predetermined area of the disk
and in the data recordable or reproducible portion in which information
such as address data or the like is not recorded. This is because a return
light quantity to the laser is set to the same condition as that in the
case of actually recording or erasing data. When the return light quantity
to the laser changes, the light emitting efficiency of the laser changes
and the laser performance cannot always be accurately measured.
On the other hand, data is not actually recorded in such an area and the
data recording is executed while always confirming addresses by a host
computer or a controller.
Measurement of the laser performance will now be described with reference
to the flowchart of FIG. 4 and FIGS. 1 and 2. When the measurement is
started (step 201), the control circuit 11 first sets a head address Addr1
of a predetermined measuring area to the address detecting circuit 10 and
drives the optical head 3 by the servo circuit 12, thereby moving the
light beam to the target address Addr1 (step 202). Next, n of a
measurement step calculating register is set to 1 (step 203). A wait is
made until the address is set to Addr1. In the signal reproduction of the
header portion of H.sub.1, if the address is set to Addr1, an address
coincidence signal is output from the address detecting circuit 10 and if
the address coincidence signal has been detected (step 204), at time
t.sub.1 in FIG. 2, a control target power of the laser beam of the control
circuit is set to a light output of P.sub.1 (step 205). The laser driving
circuit 14 monitors the power of the laser beam and controls the driving
current so as to become a predetermined power. The laser driving circuit
14 responds and the light power is set to P.sub.1 at time t.sub.2. At this
time, a timer of a time larger than t.sub.1 -t.sub.2 is made operative
(step 206). The driving current is stored into a memory (not shown)
provided in the control circuit 11 at time t.sub.3 after the light power
was sufficiently stabilized and before the address area is set to the
address area of the next sector (step 207). Such a portion exists in a
data area of D.sub.1. Thereafter, the value of n is increased one by one
(step 209). In this example, n.sub.max is set to 5 and the target light
power is set to five stages and the driving current of the semiconductor
laser when each power being output is stored into the memory.
Finally, the output of the semiconductor laser is returned to the
reproducing power (step 210). The measurement of the laser performance is
finished (step 211).
A range of the light output of five stages is set so as to satisfy a range
of the light output which is necessary when the temperature of the disk
and the relative speed between the medium and the spot at the recording
position change. A target value to be set is sequentially changed from the
low light power to the high light power. When the value of I.sub.n becomes
the maximum value at which the driving circuit can drive, this means that
the life of the laser has approached the end, so that there is a
possibility that a necessary light power is not obtained. Therefore, when
the value of I.sub.n has reached the limit value, the control circuit 11
indicates an error in the laser or informs such a laser error to other
apparatus, thereby requesting the user to exchange the laser.
The driving currents corresponding to the target light powers of P.sub.1 to
P.sub.5 are obtained as mentioned above. The target light output is
derived by supplying the driving current corresponding to the necessary
erasing or recording power to the semiconductor laser on the basis of the
value derived from the measurement point. If the light power between the
measurement points was requested, the relation between the current and the
power is linearly approximated on the basis of the result of the
measurement, thereby calculating the driving current corresponding to the
requested power.
In the invention, a measured value also can be used as an initial current
when executing the APC operation upon recording or erasing. In such a
case, the current of the value stored in the memory is first supplied to
the semiconductor laser and the APC operation is executed at the stage
when the light emission of the laser is stabilized.
In the embodiment, the laser performance has been measured in the DC
light-up mode. However, the laser light quantity upon recording is based
on the pulse light-up operation and there exists a case wherein a light
peak quantity larger than the light quantity upon erasing is necessary.
When measuring such a driving current, it is sufficient to measure by
pulse lighting up the semiconductor laser. In the case of a laser such
that the maximum rated laser outputs in the DC light-up mode and the pulse
light-up mode differ, the maximum rated output in the pulse light-up mode
is larger than that in the DC light-up mode. Therefore, in the pulse
light-up mode, the laser performance can be measured in a range wider than
that in the case of the measurement which is executed in the DC light-up
mode.
In the case of measuring in the pulse light-up mode, if the frequency of
the circuit to monitor the emission light power of the APC loop is lower
than the pulse frequency, it is sufficient that the light power
corresponding to a predetermined duty ratio of the pulse light-up
operation is calculated and the driving current corresponding to the
calculated power is measured.
When measuring in the pulse light-up mode, if the header portion is
reproduced and the address is checked, it is necessary to set the DC
light-up mode. It is desirable to set the light quantity at this time to a
low power upon reproduction. Even when measuring in the DC light-up mode,
the light quantity also can be set to the light power upon reproduction
for a time interval when the light beam is irradiated to the header
portion.
In addition to the above-described embodiment, various applications of the
invention are possible. For instance, the power of the light beam also can
be detected by receiving a part of the light beam directed from the light
source to the medium by the photodetector. The invention incorporates all
of such applications without departing from the scope of the claims of the
invention.
Top